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<script>
    //求出1-1/2 + 1/3 - 1/4 + 1/5....... 1/100的和
    var num = 0;
    for(var i = 1 ;i<101;i++){
        //判断奇数，进行加法运算
        if(i % 2 ==0){
            num -= (1/i);
            //偶数，进行减法运算
        }else if(i % 2 ===1){
            num +=  (1/i);
        }
    }
    console.log(num)
</script>